A system (such as a web application server) can accept user input through a number of components, such as through user interfaces or application programming interfaces (APIs). Validating this user input ensures that this input matches an application's data model to help protect application data from user input mistakes and from users who have malicious intent. For example, validation can occur when a user enters input into an online form having several fields. One or more of these fields can require, for example, a certain format or a set number of alphanumeric characters. If the user's input does not meet the specified requirements for that field, that input would be considered invalid.
In such an environment, there are many ways to incorporate input validations. These input validations can be independently implemented across multiple components of the system. When input validation rules are independently implemented across multiple components, inconsistencies in validation can result.